Are you not taking advantage of Jim by returning the chips after you already had a valid sales agreement worked?

Shouldn't the check have been back in the mail (With a stamp) the moment you found it in your mailbox?

By returning the chips you took advantage of Jim who sold you the chips when he may have been able to sell them to someone else in the meantime. While he has been without chips or money for several weeks, he has nothing to show for it.

If it were me, I would have sent Jim the check Overnight with a sincere apology for the oversight on your part. It is my opinion you are obligated to complete this purchase as that was what was negotiated.

Just my humble opinion of what I would consider doing "The Right Thing".

Doug